Field of the Invention
The invention relates to a method for the functional testing of turbo-machines, preferably exhaust gas turbochargers, wherein the test object is subjected to pressurized gas and is operated thereby, and to a testing device for turbo machines, preferably exhaust gas turbo-chargers, comprising a receptacle for the test object, a source for pressurized gas, preferably compressed air, to which the test object can be connected, and an evaluation unit.
The Prior Art
The systematic integration of quality assurance test stands (function test stands) in the production process of engines, transmissions and other aggregates in the automotive industry has been common practice for many years. The requirements of consumers and the legislation result in the demand for increasingly efficient engines for which, among other things, charging by means of mechanical chargers or turbo-driven chargers is used. Therefore, suitable test methods were sought also for these components. In principle, turbo-machines are rotating machines which are structured in a simple manner and, compared to, e.g., a combustion engine, have few rotating parts. Greatly simplified, it can be assumed that the machine is “OK’ if it is freely rotatable. However, in practice, many problems still occur as demonstrated, e.g., by the automobile manufacturers' error statistics for the turbochargers used or by the percentage of repairs in the operational test stands of the turbine manufacturers, which in some cases is very high. Due to the function of these fluid-flow machines, it has previously been assumed that a meaningful test of the machines is possible only near the normal operating points which requires large gas mass flows which, in addition, have to be heated (in the case of gas turbines) or are heated by the machine (in the case of turbo-compressors). The result of these requirements normally is a “classical” hot test stand in which the machines are tested in the operating range. The great disadvantages of this test at the end of the production process are late error detection, increased repair cost due to additional teardown and setup processes, increased operating costs due to multiple tests in case of an error, the risk of significant machine breakdown due to subsequent damages triggered by errors, risk of injury due to hot components and holding times for cooling the test object before fault diagnosis and fault correction can be started.
In order to avoid these problems it was a tempted in the past to perform testing of turbo-machines with compressed gas (compressed air). In doing so, it is attempted to simulate the operating points occurring in a normal operation as good as possible with a stationary gas mass flow. Due to the high energy input necessary for generating large gas mass flows, this kind of testing did not yet become widely accepted.
In the case of aircraft engines, a final testing of the completed turbo-machine takes place in most cases under operating conditions at full load, whereas in the case of high-volume products such as turbochargers for automobile engines, many times a delivery to the customer of the untested turbo-machine takes place because a complete test of all parts under operating conditions would not be economical. In EP 1 426 578 B1, a cold functional test of turbochargers in the installed state on a combustion engine is described wherein said test, just as testing under operating conditions, has the disadvantage of a late error detection. This late error detection results in the best case in increased repair costs (additional teardown and setup processes in the test stand, additional work steps during the repair due to disassembly/assembly of additional parts, re-testing after the repair) and in the worst case in serious damage to the turbo-machine due to subsequent damage triggered by the error. Therefore, there was still the demand for a cost-effective testing method which is safe in all aspects because a 100% hot testing of all turbocharger seems not to be feasible for economic reasons.
WO 2008/005679 A2 describes a method and an apparatus by means of which the performance data of a turbocharger are to be checked by testing at one or a plurality of individual operating points (single test condition). This test is intended to provide a direct comparison of operating points of the normal operation with the ones from a test stand and therefore to achieve measurement results in the test station which are comparable to the ones from a normal operation. However, no precautions are taken so as to be able to identify possible error causes through a specific adjustment of the test parameters and the operation at the borderline or outside of the normal operating range.
DE 102008031274 B3 discloses a method and a device for determining the characteristic map of a turbocharger. In the described method, an adjustable pulsation is superimposed on a constant hot gas mass flow so as to simulate in this manner the behavior of a combustion engine having one or a plurality of cylinders and therefore to be able to determine a more realistic characteristic map. The background of the method is the operation of the turbocharger with the so-called “pulse-charging” which utilizes the energy of the exhaust gas pulse when the exhaust gas valve opens. However, the principle of the test described therein does not serve for fault diagnosis or functional testing, but for determining the most realistic characteristic map on a hot gas test stand.
It was therefore an object of the present invention to provide a method and a testing device for turbo-machines which allow a simple, economical and still informative testing of these components.